The primary frontal lobe consists of three main parts: the primary motor cortex (MI), the prefrontal cortex (PF), and the nonprimary motor cortex. Each of the broad parts can be further subdivided into functionally and anatomically specialized cortical fields. Previous work on this project has shown that the nonprimary motor cortex is composed of at least two fields: the supplementary motor cortex (SM) and the premotor cortex (PM). SM and PM were differentiated from MI on the basis of neuronal responses to peripheral inputs, thresholds for evoking movements with intracortical electrical stimulation, the properties of single neurons during the performance of an operantly conditioned motor task, cytoarchitecture, and connectivity. In our physiological work, we have concentrated on one of these fields, PM, and an analysis of its neuronal activity during a variety of visual guided motor tasks. Our results support the hypothesis that PM plays a role in the visually guided behavior, especially those guided by arbitrary sensory cues, and the preparation for voluntary movements. These studies have provided new insight into the process termed behavioral set, which may underlie the ability of animals to make advantageous preparations for future actions. As such it is relevant to the finding that, in humans, deficits in the ability to change and form "sets" may reflect frontal lobe dysfunction and may underlie profound mental disorders. As such, the concept of behavioral set may provide a heuristically useful probe of frontal lobe function and represents a higher brain function amenable to both quantitative and qualitative neurophysiological analysis. Future work will be directed toward a direct analysis of PF physiology and organization, especially the interaction of frontal cortex with the basal ganglia and the dopaminergic projection to both structures.